Reflection circulator



INVENTOR HERMAN NCHAIT ATToRNEYj pril 4, 1961 H. N. cHAlT 2,978,654

REFLECTION CIRCULATOR Filed April 18, 1955 2 Sheets-Sheet 2 POSITIVE CIRCULARLY POLARZED WAV E POWER REFLECTED 0I O O INVENTOR HERMAN N. CHAIT Mab/ w fATToRNEx/ rates 2,918,654 REFLEc'noN cIRcULAToR Herman N. Chait, Washington, D.C., assignor to the United States of Americaas represented by the Secretary of the Navy The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates .to a one-way transmission system and more particularly to a one-way transmission line incorporating selective reflection.

T-R vand AT-R boxes are commonly used to provide pulse transmission systems with a means for directing energies into desired paths. Antenna and transmission systems employing these, however, suffer many disadvantages. The T-R box or gap must usually be excited with a large biasing voltage which may be of the order of 100() volts. Some power from the generator is consumed by the T-R box itself. Furthermore, such devices are not completely effective and an appreciable amount of power passes by the T-R box and into the receiver. In addition to the electrical disadvantages, antenna systems employing T-R switches are increased considerably in bulk and weight by the use of the T-R box and the necessary additional waveguide for incorporating such a device. Furthermore, the recovery time of some T-Rs limits the range of the radar. Accordingly, this invention turns to other methods of switching microwave energy.

The use of ferromagnetic materials for a device known as a circulator is described in the article by C. L. Hogan, entitled The Ferromagnetic Faraday Effect at Microwave Frequencies and its Applications-The Microwave Gyrator appearing in Bell System Technical Journal, vol. 31, pp. l-3l. In this article Hogan proposes that a one-way transmission system can be achieved with the use of a Faraday plate.

In this invention a new type of one-way transmission line hasV been devised based upon selective reflections of waves polarized in a particular sense. A ferrite slab or section is placed between quarter wave plates Within a cirform of a thin slab that fills the waveguide rather than the ferrite rod used in other and more familiar applications of the gyrator. By carefully selecting the dimensions of the ferrite section and the strength of the applied magnetic field it was found that it was possible to transmit almost all circularly polarized energy having one rotational sense and to reflect almost all circularly polarized energy having the opposite rotationalsense. Analysis made in space has shown that it is possible to have an effective ne such that the ferrite slab would appear one quarter wave thick for one rotational sense of circular polarization and one half wave thick for the other rtational sense of polarization. This-together with the highkne could explain the observed results in the waveguide. `One of the most obvious advantages of the reilectingtype circulator is that the large amounts of power developed' by the generator do` not pass through the fervrite but are reflected and only'the much smaller magnitude received energy passes through the yferrite section.

cular waveguide section. The ferrite material takes the 0 particular use of the reection circulator is illustrated a In accordance with this invention, material such as ferrite, possessing gyroscopic qualities when combined with an electrical magnetic field is inserted in the Waveguide transmission line. When a ferrite material is oriented between two quarter wave plates and placed in a waveguide and surrounded by an axial magnetic field, it has been observed that selective reflectivity of the signals applied to the waveguide occurred. With this use of certain ferrite materials it is possible to transmit almost all of the power in the waveguide polarized in one direction such as a negative circularly polarized wave and to reflect all the power sent through the waveguide that is polarized in the opposite direction such as a positive circularly polarized wave.

An object of this invention is to provide a one-way A further object of this invention is to provide a reliection type circulator for waveguide transmission in which a ferrite material is used.

A still further object of this invention is to provide apparatus that will completely reflect circularly polarized wave energy having one rotational sense and not affect circularly polarized wave energy having the opposite rotational sense.

' A still further object of this invention is to provide a ferrite slab in a waveguide surrounded by an axial magnetic field.

Another object of this invention is to provide. a ferrite reflection circulator in a waveguide that will reflect subntially all of the circularly polarized wave energy having one rotational sense and not affect circularly polarized wave energy having the opposite rotational sense.

Another object of this invention is to provide apparatus that will isolate a high frequency generator from a receiver with virtually no loss of' power in which power from a generator goes to the antenna and from the antenna to the receiver and from the receiver to the load and then back to the generator.

tion type circulator employing a ferrite section surrounded by an electromagnetic field.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

In the drawings: v v f l Fig. l of the drawings illustrates schematically an eX- emplary embodiment of this invention. a

Fig. 2 illustrates pictorially the system shown schematically in Fig. l. l

Fig. 3 is a cross-sectional view taken through theferrite slab in Fig. 2;

Fig. 4 is a graph of field current with respect to percent energy reflections as .obtained with this invention.

Referring now t'o Fig. l of the dyrawingseinpwhich a generator 11 1s shown connected through a waveguide section 13 to a microwave coupler 15. Aniantenna Y17 Another object of this invention is to provide a reiiecamasar 3,. wave plates 39 and 41. A control unit 43 is provided for said magnetic field. The section of circular waveguide containing the ferrite slab is designated 37 in the drawings. I

For purposes of illustration it'will now be yassumed that the ferrite section will reect positive circularly polarized energy and will p-ass negative circular-ly polarized energy. In operation the energy produced by the generator 11 will pass along or through waveguide section 13 and into the microwave coupler 15. From here` the energy will go into the waveguide portion. The energy will travel through quarter wave plate 39 and then to the ferrite section 37. Here the energy will be almost completely reflected and sent back through the quarter wave plate 39, through the waveguide 35 and into the microwave coupler 15. From here the energy travels out waveguide section 19 and is radiated into space by the antenna 17. Retiections of the radiated energy will be then picked up by antenna 17 and passed along waveguide section 19 into the microwave coupler 15. The received energy is then passed along into the waveguide 35 through quarter wave plate 39 and thence to the ferrite section. The received energy is polarized opposite to the transmitted energy and will pass thnough the ferrite section as though it were not there. From there the received energy passes through quarter wave plate 41, the microwave coupler 25 and thence through waveguide section23 to the receiver 21. Control unit 43 serves .to apply a controllable amount of electromagnetic field about the ferrite section 37 to control its operation.

The invention may be more clearly understood by reference to Fig. 2 which shows a specific embodiment of the block diagram of Fig. 1.

Referring now to Fig. 2 of the drawings in which the physical location of the circuit elements illustrated schematically in Figure 1 is shown, the microwave couplers and 25 are similar to magic Ts commonly used in waveguide systems. wave coupler is made up of a chamber of circular crosssection and adapted to receive rectangular waveguides of horizontal or vertical orientation. The ferrite element 101 as well as quarter plates 39 and 41 are inserted within a continuous circular waveguide portion 35. The ferrite element 101 is located in the center portion between quarter wave plates 39 and 41. The ferrite section 37 is comprised of the ferrite element 101 located within the vcircular waveguide 3S and a continuous coil 103 wrapped around the circumference ofthe circular waveguide 35 adjacent the ferrite` Connected to coils 103 are wires .105 and 107 connected to a variable or fixed source of energizing voltage from the control unit 43. The ferrite element 101 has a lengthand a thickness which is critical for the proper operation of the reflecting circulator. The width of the ferrite element 101, as shown more clearly in Fig. 3, is the same as the inner diameter of the circular waveguide 35. In other words,` the ferrite section extends completely across the waveguidev or spans the'diarneter. The lengthV of the ferrite section in a preferred embodiment is .50 inch.

The operation'of the system can more readily be-understood from the pictorialv representation in Fig. 2. .The v energy generated by the generator v11 is vertically pola- :rized and when it reaches the microwave coupler 15 through waveguide 13 adapted for vertical polarization its most rfavorable direction is-into circular waveguide In this particular system the micro- `35. As the vertically. polarized energy travels past the Yquarter wave plate 39, the vertical polarization is con- 'andthe energy -upon 'traveling bach-through the quarter verted to circularlyfpolarized wave 'energy of a selected through the ferrite section.

wave plate 39 is converted into a horizontally polarized wave. After entry into the microwave coupler 15, the horizontally polarized energy passes into the waveguide 19 adapted for horizontally 'polarized energy and from thence to the antenna whereupon radiation into space occurs. The antenna also receives energy from space and consequently portions of the radiated energy that are reflected by targets or other objects accepted by the antenna and passed through the waveguide 19 into microwave coupler 15. The received energy, being horizontally polarized, is rejected by vertical guide 13 and will enter the waveguide 35. Because the received energy is orthogonally polarized from the generator energy originally passed to the right through the quarter wave plate 39, the quarter wave plate will convert this received energy into circularlypolarized wave energy having the opposite rotational sense with respect to the energy from the generator. Since the ferrite section will not react with circularly polarized wave energy of this opposite rotational sense, the received energy will pass through the ferrite section unaffected by it. When the received energy passes through the quarter wave plate `41, it will become horizontally polarized because of the orientation selected for the quarter wave plate. From the microwave coupler the horizontally polarized received energy will be -passed by waveguide 2.3 to receiver terminal where information is detected from the energy thus received.

in Fig. 3 the waveguide 35 is shown in cross-section taken along the lines 3-3 of Fig. 2. Fig. 3 is taken through the center of the ferrite slab 101 and clearly shows its preferred width dimensions with respect to waveguide 35.

' Referring to Fig. 4 ofthe drawings, a chart indicating the relationship between the reectedpower and the magnetic field strength is shown for a preferred embodiment of this invention. The vertical displacement indiicatas power or energy retiected by the ferrite in terms of the percent of the total energy or power applied to the ferrite section. The horizontal displacement indicates the magnetic ield current applied in terms of amperes. Line 201 shows the relationship between the percent of the power reflected and the magnetic current for energy passing through the waveguide. Line 203 shows the relationship between the percent of the power reiiected and the magnet current for circularly polarized wave energy of the-selected rotational sense.

In a particular embodiment the material for the ferrite section was -a slab of Ferrmic No. 1331, and having a diameter of 0.935 inch and 0.60 inch in thickness.A For a range of magnet current from 9 to ll amperes it is found that about of the positively circularl-y polarized energy and less than 5% of negative circularly polarized energy is reected. A circuit employing a reection circulatorY was tested at 9375 mc. and a loss o-f 0.5 db from the generator to the antenna was observed yand a loss of 0.2 db from the antenna to the receiver was observed. Y Y

The microwave coupler 25 may be equipped with auxiliary devices such as a T-R and AT-R boxes to facilitate the utility of the system-employing ferrite sections. As an example aT-R box could be used to protect the receive-r Vfrom excessive amounts of energy that may pass Such excessive energy after arriving at microwave coupler 25 would be reected from the l`-R box and ythence into the ferrite section where the energy again wouldbe reected and passed back :through the microwave coupler 2.5 into the load 27 where it would be absorbed. l 1

It shouldbe understood, of course, that the foregoing disclosure relates only vto a preferred embodiment of the invention and that "itis intended to cover all changes and modifications offthe examplesof the invention herein lchosen for the purposes ofthe disclosure,which do not constitute departure" from the spirit and scope Aof `the invention set forth in l the appended claims.

What is claimed is: 1. A reection type circulator comprising a wave energy proportioned Yto substantially ll the cross-sectional area of said waveguide section,

with respect to said second and third ports and to convert linearly polarized wave energy from said third port of said coupling means into circularly polarized wave energy having said one rotational sense 6 of reference direction and to convert linearly polarized wave energy from said second waveguide section is received thereby.

2. The circulator as described in claim 1 wherein said wave energy conversion means is of the quarter wave plate variety.

3. The circulator as described in claim 2 wherein said wave energy utilization means includes, as the input thereof, wave energy conversion means for converting circularly polarized wave energy passing through said ferrite slab into linearly polarized wave energy.

References Cited in the le of this patent UNITED STATES PATENTS 2,644,930 Luhrs July 7, 1953 2,755,447 Englemann July 17, 1956 2,768,354 Hogan Oct. 23, 1956 2,798,205 Hogan July 2, 1957 2,817,812 Fox Dec. 24, 1957 2,954,535 Porter Sept. 27, 1960 OTHER REFERENCES Proceedings of the IRE, January Frequencies, 1, Jan. 1953, 

